1. Field of the Invention
The present invention relates to promoter regions, under whose control transgenes can be epidermis-specifically expressed in plants. Furthermore, the invention relates to recombinant nucleic acid molecules, which comprise said promoter regions, and to transgenic plants and plant cells, which have been transformed by means of said nucleic acid molecules, as well as to methods for their generation. Furthermore, the present invention relates to nucleic acid molecules comprising a promoter according to the present invention, and to nucleic acid sequences or transgenes, which are capable of mediating pathogen resistance, as well as to plants and plant cells transformed by means of said nucleic acid molecules, and to methods for their generation.
2. Description of Related Art
Those DNA regions of a gene, which are located upstream of the transcription initiation point and by which the initiation point and the initiation frequency of the transcription and thus the expression level and the expression pattern of the controlled gene are determined, are in general referred to as promoters. RNA polymerase and specific transcription factors activating the RNA polymerase bind to the promoters in order to initiate transcription together with the basal transcription complex. The effectiveness of the promoters is often enhanced and regulated by additional DNA sequences, the enhancer sequences, whose position, contrarily to the position of the promoters, is not fixed. These regulatory elements can be located upstream, downstream, or in an intron of the gene to be expressed.
In recombinant DNA technology, promoters are inserted into expression vectors in order to control the expression of a transgene, which is normally not the gene naturally regulated by the promoter. Of substantial significance herein is the specificity of the promoter, which determines at which point in time, in which types of tissue, and at which intensity a gene transferred by means of genetic engineering is expressed.
In plant breeding, recombinant DNA technology is often used for transferring specific advantageous properties to useful plants, which is supposed to lead to a higher yield, for example by means of increased pathogen resistance, or to improved properties of the harvest products. Herein, it is often desirable that the transferred gene be not expressed ubiquitously, but only in those tissues, where the transgenic activity is desired, as the presence of the transgenic product can have a negative effect on normal physiological processes in some tissues. Thus, it could, for example, be shown that the overexpression of an anionic peroxidase under the control of the ubiquitously effective 35S promoter leads to wilting of transgenic tobacco plants, as less root growth occurs and therefore also less root mass is developed (Lagrimini et al. (1997) The consequence of peroxidase overexpression in transgenic plants on root growth and development. Plant Mol Biol. 33 (5), S. 887-895). The overexpression of the spi2 peroxidase under the control of the likewise ubiquitously effective ubiquitin promoter, leads to reduced epicotyl development and reduced longitudinal growth in comparison with control plants (Elfstrand, M. et al. (2001) Overexpression of the endogenous peroxidase-like gene spi2 in transgenic Norway spruce plants results in increased total peroxidase activity and reduced growth. Plant Cell Reports 20 (7), S. 596-603). Irrespective of negative effects on physiological processes, it is often supposed to be prevented in resistance breeding that the transgenic product is also present in the harvested plant parts.
Therefore, promoters functioning either tissue-specifically or inducibly have been isolated during the past years. Tissue-specific promoters are, for example, seed-, tuber-, and fruit-specific promoters. The inducible promoters can be activated, for example, by means of chemical induction, light induction, or other stimuli.